A Computational Approach for the Prediction of Fatigue Behaviour in Peripheral Stents: Application to a Clinical Case

Nickel-Titanium (NiTi) peripheral stents are commonly used for the treatment of diseased femoropopliteal arteries (FPA). However, cyclic deformations of the vessel, induced by limb movements affect device performance and fatigue failure may occur. Stent strut fracture has been described in the literature, and is implicated as a potential causative factor in vessel re-occlusion. In this paper, a numerical approach is proposed to predict the fatigue behaviour of peripheral NiTi stents within patient-specific arterial geometries, as additional information to aid clinician intervention planning. The procedure needs some patient-specific vessel features derived from routine clinical images but, when this information is not available, reference data from the literature may be used, obviously increasing the uncertainties of the results. In addition, specific stent material data are required and can be obtained from experimental tests. Several 3D finite element models resembling stented vessel segments are built and used for fatigue analyses. For each model, axial cyclic boundary conditions are obtained from a patient-specific lumped parameter model representing the entire artery as a series of suitable springs. This allows the simplification of stiffness changes along the vessel due to plaque and stent that affect local axial deformations. Imposed local cyclic bending values depend on the stent location along the FPA. The procedure is exemplified by its application to an actual clinical case that showed two strut fractures at 18 months follow-up. Interestingly, despite the lack of some of patient-specific information and the use of data from the literature to inform the model, the numerical approach was able to interpret the in vivo fractures.